Canopus was the code name for France’s first two-stage thermonuclear test, conducted on August 24, 1968 at Fangataufa atoll in French Polynesia.
In 1966, France was able to use fusion fuel to boost plutonium implosion devices with the Rigel shot. Roger Dautry, a nuclear physicist, was selected by the CEA to lead the development effort to construct a two-stage weapon. France did not have the ability to produce the materials needed for a two-stage thermonuclear device at the time, so 151 tons of heavy water was purchased from Norway and an additional 168 tons from the United States. This heavy water went into nuclear reactors in 1967 to produce tritium needed for the device.
The announcement by France in the late 1960s to test a hydrogen bomb provoked the People’s Republic of China to conduct a full scale hydrogen bomb test of its own on June 17, 1967.
France was to test the new device as part of a 5 shot series conducted at the nuclear testing grounds in French Polynesia. The device weighed three tons and used a lithium deuteride secondary stage with a highly enriched uranium jacket primary.
Fangataufa was selected as the location of the shot due to its isolation in respect to the main base on Mururoa. The device was suspended from a large hydrogen filled balloon. It was detonated at 18:30:00.5 GMT with a 2.6 megaton yield at an altitude of 1800 feet. As a result of the successful detonation, France became the 5th thermonuclear nation.